Glossary

Optical systems that are between a few micrometres (millionths of a metre) and one millimetre in size, including small lenses or arrays of lenses.

Lines, symbols, designs, images or numbers that are printed at dimensions barely perceptible to the unaided human eye but visible at magnifications of between x5 and x10 by (say) a jeweller’s loupe. Microprinting on banknotes usually combines positive and negative characters.

The very small scale structure of a prepared surface of a material as revealed by a microscope above 25× magnification. Diffractive microstructures comprise microprotrusions or microgrooves, or a combination thereof, which are capable of diffracting lightwaves.

A diffractive image in which different, usually unrelated images appear at different viewing angles. The most usual, and easiest to make, are images that flip from one to another as a DOVID is tilted from side to side. The most difficult is an image that changes as the DOVID is rotated.

Captures image data within specific wavelength ranges across the electromagnetic spectrum. The wavelengths may be separated by filters or detected with the use of instruments that are sensitive to particular wavelengths, including light from frequencies beyond the visible light range (ie. infrared and ultraviolet). Multispectral imaging can allow extraction of additional information the human eye fails to capture with its visible receptors for red, green and blue. 

A unit of measurement commonly used in authentication when referring to the thickness or gauge of physical substrates and features. One nanometre is equal to one billionth (10-9) of a metre.

The science and technology of precisely manipulating the structure of matter at the atomic and molecular level. In the authentication sector, nanotechnology is used to explore and develop unique optical phenomena for use in new material and security features.

A wave reflected from an object and incident on a usually photosensitive material. Also refers to the beam that is transmitted and diffracted by a holographic plate (H1) which becomes the ‘object’ from which a copy (H2) is made. See also Reference beam.

The off-axis method is an origination technique where a laser beam is split into two beams: an object and a reference beam. The object beam illuminates the object/artwork and is scattered onto a photoresist. The reference beam is directed onto the photoresist from the same side but at a different angle (off-axis). The two beams meet and overlap at the photoresist, generating an interference pattern which, in essence, provides a three-dimensional holographic record of the object.

Overt and semicovert security features with dynamic characteristics that change according to the viewing angle – eg. from one colour to another, or from one image to another.

Process to check security features visible with simple smartphone cameras, such as diffractive motion effects based on the viewing angle.

Allows static controls using cameras at multiple wavelengths (visible and infrared light).

Security features such as holograms that are apparent to the human senses – especially those of sight and touch – without the need for additional readers and instruments. Such features are designed to enable all stakeholders, including the public, to identify if something is genuine or not.

The phenomenon in an image which allows depth to be judged from the movement of near image elements relative to more distant ones. Traditional embossed holograms only display parallax from side to side, but the lack of vertical parallax is rarely noticed. Ortho-parallax is the term for when the movement of the elements is in a counterintuitive direction (ie. 90°) to the angle of view.

A security feature that requires an action such as scanning or photocopying to become visible. See also Active security feature.

A type of fluorescence that continues for a period of time after the stimulus that produced the emission has stopped.

A light-induced reversible colour change which in its most familiar form involves an ultraviolet-induced transformation from colourless to coloured. Sunglasses that darken in the sunlight and revert to near colourless in subdued light constitute the most widely known application of photochromism. However, there are a diverse range of other applications and potential applications that include fuel markers, security inks and electronic nanotechnology.

Luminescence produced by exposure to ultraviolet light.

Holograms produced from materials that polymerise (combine to form a polymer) under the action of light energy and thus change their refractive index. Used to record volume reflection holograms (see Volume hologram).

A light-sensitive material used in processes such as photolithography and photoengraving to form a patterned coating on a surface. A substrate is coated with a light-sensitive organic material. A patterned mask is then applied to the surface to block light, so only unmasked areas are exposed. A solvent, called a developer, is then applied to the surface. In the case of a positive photoresist, the photo-sensitive material is degraded by light and the developer dissolves away exposed areas, leaving a coating where the mask was placed. In the case of a negative photoresist, the photo-sensitive material is strengthened (either polymerised or cross-linked) by light, and the developer dissolves away areas not exposed to light, leaving a coating in areas where the mask was not placed. This process is used to create surface grating images, which are the first stage in producing embossed holograms.

The illegal reproduction and distribution of copyright material, generally taken to be audio and video content.

In digital imaging, a pixel (or picture element) is the smallest item of information in an image. Pixels are arranged in a 2D grid, represented by squares. Each pixel is a sample of an original image, with more samples typically providing more accurate representations of the original.

Plasma is superheated matter – so hot that the electrons are ripped away from the atoms, forming an ionised gas. It comprises over 99% of the visible universe. In the night sky, plasma glows in the form of stars. That branch of lightning that cracks the sky is plasma. So is the sun… and so are neon signs on city streets. Plasma is often called ‘the fourth state of matter’, along with solids, liquids and gas. Just as a liquid will boil, changing into a gas when energy is added, heating a gas will form a plasma – a soup of positively charged particles (ions) and negatively charged particles (electrons).

In physics, a plasmon is a quantum of plasma oscillation. Just as light consists of photons, the plasma oscillation consists of plasmons. The plasmon can be considered as a quasiparticle since it arises from the quantisation of plasma oscillations,

The generation, detection, and manipulation of coherent electron oscillations (known as surface plasmon polaritons), as they travel together with an electromagnetic wave along the interface between a metal (eg. silver, gold) and a dielectric material (eg. glass, air) at the nanometric scale. Inspired by photonics, plasmonics follows the trend of miniaturising optical devices, and can be applied as a security feature. The plasmons can be controlled through careful modelling and application of, among other things, the dielectric and metal layer thickness in a ‘sandwich’ structure. When the sandwich structure is applied as a device to a security document, it allows light that falls on the surface of the device to be controlled in terms of its wavelength (allowing control over the colour) and amplitude (giving rise to the intensity, or brightness of the colour generated).

The alignment of the electric and magnetic fields in a particular orientation in a lightwave. If all the waves in a beam of light move up and down or from side to side together, the beam is said to be plane-polarised. Some materials have the ability to filter out all lightwaves except those in a particular direction. Other materials are said to be optically active if they are able to change the angle of a plane-polarised beam of light. Liquid crystals often have this property and this enables them to be detected.

An optical device which transforms unpolarised light into polarised light. It is used to examine light reflected from ink or thin-film coating. It blocks light rays of a specific polarisation direction while letting light rays of other polarisation directions pass.

A thermoplastic polymer resin of the polyester family, used to make the most common container in the soft drink market today: the plastic bottle. Also used as the base material for most surface-applied holograms and security threads.

A substance or material consisting of very large molecules, or macromolecules, composed of many repeating subunits. Plastic and polyester are all polymers. Polymer banknotes were first introduced in Australia and are widely used around the world.

A laboratory technique for rapidly producing (amplifying) millions to billions of copies of a specific segment of DNA, which can then be studied in greater detail.

A label construction made up of three layers: a face material, a pressure-sensitive adhesive, and a backing sheet coated with a release agent. Pressure-sensitive labels only need the pressure of a hand to be applied to an item.

A cooperative arrangement between two or more public (ie. government) and private sector entities.

A rainbow is the visual result of splitting white light into its constituent colours according to wavelength. The order of the colours is red, orange, yellow, green, blue, indigo, violet – with red having the longest wavelength and violet the shortest. The natural phenomenon is caused by the prismatic effect of raindrops in the sky but it can also be caused by diffractive gratings with a spatial frequency approaching the wavelength of light.

When illuminated with incandescent (white) light, rainbow holograms display images bathed in a changing rainbow spectrum of colours as the viewer moves their eyes up and down. Holographers have developed considerable control over the colours displayed in this type of hologram to produce images in a specific colour or in near natural colour.

A non-destructive analytical technique used to identify and study the molecular composition and structure of materials. It works by detecting molecular vibrations, which provide unique spectral fingerprints for different substances. Named after Indian physicist C V Raman, who discovered the Raman Effect, this technique is widely used in chemistry, materials science, biology, and other fields for analysing a wide range of substances.

A 2D picture represented as a rectangular grid of pixels.

The task of converting a vector graphic image into a raster image (ie. a series of pixels, dots or lines which recreate the vector image). The higher the resolution, the greater the number of pixels per unit area. Raster images are used for ensuring a smooth transition of colours and shades, with the most common use being for processing photos. The most popular raster graphics editor is Photoshop.

A ‘step and repeat’ process whereby a single diffractive image is laid out in rows and columns in preparation for shim production. It can either be carried out mechanically or optically. In the mechanical process, the single image is made into a stamper which is impressed at predetermined intervals, into a plastic sheet. If done optically, the single image is exposed in a predetermined pattern onto a (glass) plate coated with a photoresist.

A system representing the colours used on a digital display screen. Red, green and blue can be combined in various proportions to obtain any colour in the visible spectrum.

An unmodulated beam which, when directed at a photoresist forms a stationary interference pattern with the object beam. See also Object beam.

The bouncing of light off an object (as opposed to light that transmits through or is absorbed by an object).

A hologram that is viewed by the reflection of white light. The diffractive planes within the depth of the recording material have a spacing which corresponds only to a single wavelength of light. This wavelength, usually green or yellow, is reflected back and reconstructs the image, the other colours being transmitted and absorbed by a black backing placed behind the hologram.

The bending of light as a beam passes from one medium (say air) to a different medium (say glass). For applications of refraction see High refractive index.

A common business process for collecting written information about the capabilities of various suppliers. Normally, an RFI follows a format that can be used for comparative purposes. An RFI is primarily used to gather information to help make a decision on what steps to take next. RFIs are therefore seldom the final stage of procurement and are instead often used in combination with a request for proposal (RFP) and request for quotation (RFQ).

A document that solicits a proposal from suppliers, often as part of a bidding process, by an agency interested in procuring a commodity or service. An RFP is used when a general need or problem must be solved, and potential sellers are proposing solutions and how much they will cost. Companies evaluating an RFP must consider not only the cost but the effectiveness of the solution.

A document that solicits quotations from suppliers often as part of a bidding process, by an agency interested in procuring a commodity or service. An RFQ is used when a quote is needed for a specific need and solution.

Occurs when a surface returns a large portion of directed light back to its source, from a much wider angle than a reflective surface. Retroreflective material is made using microlenses (microspheres).

Polyester threads that are either fully or partially embedded down the length of paper during the paperforming process. Fully embedded threads – typically less than 1.8mm wide – can only be viewed when the document is held up to the light. Partially embedded threads appear intermittently on one side of the paper. Their size is typically up to 4mm wide and they act as carriers for a range of overt security features.

A security feature requiring simple, sometimes commercially available tools to view it, such as ultraviolet (UV) lights, polarising filters, magnifiers and lenses. The examiner needs to know where the features are and how to examine them and they are not normally made known to the general public.

The application of a unique identifier to each unit in a lot or batch. The identifiers are numbers but might be printed as alphanumerics or barcodes or might be embedded in a chip activated by radio frequency (RFID). The numbers may be sequential or randomly generated; what is important is that the same number should not be used twice.